The invention relates to a coupling hook, especially for the lower steering arms of a three-point attaching device of a tractor. The coupling has a hook body, a locking pawl spring-loaded towards the locking position and means for moving the locking pawl into the open position. The hook body includes a bearing recess, open towards one end, for the bearing ball of an implement to be attached, a recess for receiving the locking pawl, an aperture for allowing part of the locking pawl to enter the region of the bearing recess, a first stop face provided by the face of the aperture arranged towards the open end of the bearing recess, a second supporting stop arranged at a distance therefrom, and a locking stop arranged away from both stops in the direction of the bearing recess to secure the locking pawl in the locking position.
The locking pawl, on its upper face, includes a first supporting face cooperating with the first stop face. On its underside, it includes a second supporting face cooperating with the second supporting stop. Towards its rear end, it includes a locking face cooperating with the locking stop. At its front end entering the bearing recess, it includes an unlocking face. Also, the locking pawl includes a projection which projects downwardly beyond the second supporting face to limit the setting movement of the locking pawl and a locking face to arrest the bearing ball in the bearing recess.
A coupling hook is described in U.S. Pat. No. 4,126,057, issued Nov. 21, 1978. A coupling hook part projects outwardly from a through-aperture. The projecting part of the coupling hook is provided with an actuating cable for opening the locking pawl. However, this design of the locking pawl and the way it is supported relative to the locking stop are such that if the locking pawl is subject to any influences when in operation, for instance if it is affected by the bearing pin or by branches or the like, the locking pawl may open.